Zoom optical system

ABSTRACT

A zoom optical system comprising, in order from the object side, a first lens unit having positive refractive power, a second lens unit having positive refractive power and a third lens unit having negative refractive power, and configured to change a magnification from a wide position to a tele position by moving the lens units on the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, thereby having a short total length at the tele position in particular and favorable optical performance.

[0001] a) Field of the Invention

[0002] The present invention relates to a zoom optical system forphotographic cameras, and more specifically a zoom optical system forlens shutter cameras in particular.

[0003] b) Description of the Prior Art

[0004] Lens shutter cameras have generally used zoom lens systems inrecent years and demands are increasing in particular for lens systemswhich have vari-focal ratios of 3 and higher. On the other hand, demandsare increasing for compact and inexpensive lens systems.

[0005] Out of various types zoom lens systems for lens shutter cameraswhich are known as those having vari-focal ratios of 3 and higher inparticular, there are known many zoom lens systems each composed ofthree lens units having a positive-positive-negative refractive powerdistribution. The zoom lens system which is composed of the three lensunits consists in order from the object side, for example, of a firstlens unit having positive refractive power, a second lens unit havingpositive refractive power and a third lens unit having negativerefractive power, and is configured for zooming from a wide position toa tele position by moving the lens units so as to widen an airspacebetween the first lens unit and the second lens unit and narrow anairspace between the second lens unit and the third lens unit.

[0006] An conventional examples of such a zoom lens system as thatdescribed above, there are known zoom lens system which are disclosed byJapanese Patents Kokai Publication No. Hei 11-183801, No. Hei 11-119098,No. Hei 11-52232, No. Hei 9-179025, No. Hei-9-120028, No. Hei 9-90225and No. Hei 8-262325. These conventional examples have large totallengths at tele positions, thereby requiring complicated and large lensbarrels.

[0007] Furthermore, a zoom lens system disclosed by Japanese PatentKokai Publication No. Hei 9-33813 has a high telephoto ratio, therebyhardly allowing cameras to be configured compact.

[0008] Furthermore, a zoom lens system disclosed by Japanese PatentKokai Publication No. Hei 8-152559 requires high precisions forairspaces and the like, thereby being hardly manufactured.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a zoom lenssystem comprising, in order from the object side, a first lens unithaving positive refractive power, a second lens unit having positiverefractive power and a third lens unit having negative refractive power,and configured to change a magnification from a wide position to a teleposition by moving the lens units on the object side so as to widen anairspace between the first lens unit and the second lens unit and narrowan airspace between the second lens unit and the third lens unit, andsatisfy the following conditions (1), (2), (3) and (4):

[0010] (1) fT/fW>3.8

[0011] (2) 0<[S(fTa)·S(fW)]/(fTa−fW)<0.2

[0012] (3) 0.8<L(fTa)/(fTa−fW)<1.05

[0013] (4) 0<H(G1)/fTa<0.023

[0014] Another object of the present invention is to provide a zoomoptical system comprising, in order from the object side, a first lensunit having positive refractive power, a second lens unit havingpositive refractive power and a third lens unit having negativerefractive power, and configured to change a magnification from a wideposition to a tele position by moving the lens units on the object sideso as to widen an airspace between the first positive lens unit and thesecond lens unit and narrow an airspace between the second lens unit andthe third lens unit, wherein the first lens unit consists of, in orderfrom the object side, a negative meniscus lens element which has aconcave surface on the object side and a positive lens element which hasan object side surface having curvature higher than that of an imageside surface, and wherein the third negative lens unit comprises, inorder from the object side, a biconcave lens element, positive lenscomponent which has an object side surface having curvature higher thanthat of an image side surface and a negative lens component which hascurvature on an object side concave surface higher than that on an imageside surface, and satisfies the following conditions (2A) and (3A):

[0015] (2A) 0<[S(fT)−S(fW)]/(fT−fW)<0.2

[0016] (3A) 0.8<L(fT)/(fT−fW)<1.05

[0017] Still another object of the present invention is to provide azoom optical system comprising, in order from the object side, a firstlens unit having positive refractive power, a second lens unit havingpositive refractive power and a third lens unit having negativerefractive power, and configured to change a magnification from a wideposition to a tele position by moving the lens units on the object sideso as to widen an airspace between the first lens unit and the secondlens unit and narrow an airspace between the second lens unit and thethird lens unit, wherein the third negative lens unit comprises, inorder from the object side, a biconcave lens component, a positive lenscomponent which has an object side surface having curvature higher thanthat of an image side surface and a negative lens component which has anobject side concave surface having curvature higher than that of animage side surface, wherein at least an airspace between the second lensunit and the third lens unit is changed for focusing, and wherein thezoom optical system satisfies the following condition (10):

[0018] (10) (β3T)²/[F(T)×0.03]<60

[0019] Still another object of the present invention is to provide anoptical system comprising, in order from the object side, a first lensunit having positive refractive power, a second lens unit havingpositive refractive power and a third lens unit having negativerefractive power, and configured to change a magnification from a wideposition to a tele position by moving the lens unit on the object sideso as to widen an airspace between the first lens unit and the secondlens unit and narrow an airspace between the second lens unit and thethird lens unit, change the airspace between the second lens unit andthe third lens unit for focusing, and satisfies the following conditions(1), (4), (5) and (6):

[0020] (1) fT/fW>3.8

[0021] (4) 0<H(G1)/fTa<0.023

[0022] (5) 15<(β3T)²−(β3T)²×(β2T)²<27

[0023] (6) 0.3<f1/fTa<0.5

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 through 12 are sectional views showing compositions offirst through twelfth embodiments of the present invention;

[0025]FIG. 13 shows curves visualizing aberration characteristics at awide position of the first embodiment;

[0026]FIG. 14 shows curves visualizing aberration characteristics at anintermediate focal length of the first embodiment;

[0027]FIG. 15 shows curves visualizing aberration characteristics at atele position of the first embodiment;

[0028]FIG. 16 is a perspective view of a compact camera which uses thezoom optical system according to the present invention; and

[0029]FIG. 17 is a sectional view of the compact camera which uses thezoom optical system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] A zoom optical system according to the present invention (zoomoptical system having a first composition) is characterized bycomprising, in order from the object side, a first lens unit G1 havingpositive refractive power, a second lens unit G2 having positiverefractive power and a third lens unit G3 having negative refractivepower, for example, as shown in FIG. 1, changing a magnification from awide position to a tele position by moving the lens units G1, G2 and G3on the object side so as to widen an airspace between the first lensunit and the second lens unit and narrow an airspace between the secondlens unit and the third lens unit, and satisfying the followingconditions (1), (2), (3) and (4):

[0031] (1) fT/fW>3.8

[0032] (2) 0<[S(fTa)−S(fW)]/(fTa−FW)<0.2

[0033] (3) 0.8<L (FtA)/(FtA−Fw)<1.05

[0034] (4) 0<H (g1)/fTa<0.023

[0035] wherein reference symbols fT and FW represent focal length of thezoom optical system at the wide position and the tele positionrespectively, a reference symbol fTa designates an optical focal lengthin a focal length region exceeding 3.8 times of the focal length at thewide position, a reference symbol S(w) denotes a distance as measuredfrom a most object side surface to a most image side surface at the wideposition, a reference symbol S(fTa) represents a distance as measuredfrom a most object side surface to a most image side surface at thefocal length of fTa, a reference symbol L(fTa) designates a distance asmeasured from the most object side surface to the most image sidesurface at the focal length of fTa and a reference symbol H(G1) denotesa distance as measured from the most object side surface to a frontprincipal point of the first lens unit G1.

[0036] In order to obtain a high vari-focal ratio, the zoom opticalsystem according to the present invention is configured comprise thefirst positive lens unit G1, the second positive lens unit G2 and thethird negative lens unit G3, and change the magnification from the wideposition to the tele position by moving all the lens units G1, G2 and G3on the object side so as to widen the airspace between the first lensunit G1 and the second lens unit G2 and narrow the airspace between thesecond lens unit G2 and the third lens unit G3.

[0037] For a reason which is described next, the zoom optical systemaccording to the present invention is configured to satisfy the abovementioned conditions (1), (2), (3) and (4).

[0038] The condition (1) defines a zoom ratio of the zoom optical systemaccording to the present invention and if a lower limit of 3.8 of thiscondition is exceeded, it will be impossible to obtain the object zoomoptical system which has a high vari-focal ration.

[0039] If the condition (1) is not satisfied, a denominator (fTa−fW)will have a small value in the conditions (2) and (3) and it will bedifficult to compose a lens system so as to satisfy these conditions.

[0040] The condition (2) defines a ratio of a variation amount of adistance as measured from a first surface (a most object side surface)of the optical system to a final surface (a most image side surface)caused by changing a focal length from fW to fTa for zooming relative toa variation amount of a focal length of the optical system as a wholecaused by changing the focal length from fW to fTa for zooming and if alower limit 0 of the condition (2) is exceeded, a correction sensitivityof a back focal position to a positional deviation of a lens surface ina direction of an optical axis will be high that is, a deviation of thelens surface in the direction of the optical axis will result in a largepositional deviation of the back focal position, whereby imagingperformance will tend to be easily lowered. If an upper limit of 0.2 ofthe condition (2) is exceeded, in contrast, each lens unit will have aweak power, thereby making it difficult to obtain a required vari-focalratio when the optical system is configured so as to have a short totallength. Furthermore, when the optical system is to be focused by movingsome of the lens units in a direction along the optical axis, the lensunits must be moved for long distances, thereby making it impossible tofocus the optical system on an object located at an extremely shortdistance.

[0041] It is more desirable to satisfy, in place of the condition (2),the following condition (2-1) which has an upper limit of 0.07.

[0042] (2-1) 0<[S(fTa)−S (fW)]/(fTa−fW)<0.07

[0043] The condition (3) defines a ratio of a total length of theoptical system in a telephoto condition (at the focal length fTa)relative to a variation amount of a focal length of the optical systemas a whole (a variation amount of the focal length from the wideposition to the focal length fTa) and if a lower limit of 0.8 of thecondition (3) is exceeded, optical performance will be remarkablylowered due to remarkable variation of spherical aberration, coma andlongitudinal chromatic aberration and the like which are caused byzooming. If an upper limit of 1.05 of the condition (3) is exceeded, atelephoto ratio [L(fTa)/fTa] will be enhanced, thereby making itimpossible to shorten a total length of the optical system.

[0044] It is more desirable to satisfy, in place of the above-mentionedcondition (3), the following condition (3-1) which has an upper limit of1.04 and a lower limit of 0.9:

[0045] (3-1) 0.9<L (fTa)/(fTa−fW)<1.04

[0046] The condition (4) defines a ratio of the distance [H(G1)] asmeasured from the most object side surface to the front principal pointof the first lens unit G1 relative to the focal length (fTa) of theoptical system as a whole in the telephoto condition. If a lower limitof 0 of the condition (4) is exceeded, the telephoto ratio L (fTa)/fTawill be enhanced, thereby making it impossible to configure the opticalsystem compact by shortening its total length. If an upper limit of0.023 is exceeded, aberrations, distortion in particular, will beovercorrected.

[0047] It is more desirable to satisfy, in place of the condition (4),the following condition (4-1) which as a lower limit of 0.01 and anupper limit of 0.02.

[0048] (4-1) 0.01<H(G1)/fTa<0.02

[0049] A zoom optical system which has a second composition according tothe present invention is an optical system comprising, in order from theobject side, a first lens unit G1 having positive refractive power, asecond lens unit G2 having positive refractive power and a third lensunit G3 having negative refractive power, and configured to change amagnification from a wide position to a tele position by moving the lensunit on the object side so as to widen an airspace between the firstlens unit G1 and the second lens unit G2 and narrow an airspace betweenthe second lens unit G2 and the third lens unit G3, wherein the firstlens unit G1 having the positive refractive power consists of two lenselements, in order from the object side, a negative meniscus lenselement having a concave surface on the object side and a positive lenselement which has curvature on an object side surface higher than thaton an image side surface, and the third negative lens unit G3 having thenegative refractive power comprises, in order from the object side, anegative biconcave lens element, a positive lens element which hascurvature on an object side convex surface higher than that on an imageside surface and a negative lens element which has curvature on anobject side concave surface higher than that on an image side surface,and the zoom optical system satisfies the following conditions (2A) and(3A):

[0050] (2A) 0<[S (fT)−S (fW]]/(fT−fW)<0.2

[0051] (3A) 0.8<L (fT)/(fT−fW)<1.05

[0052] wherein reference symbols fW and fT represent focal lengths ofthe zoom optical system as a whole at the wide position and the teleposition respectively, a reference symbol S (fW) designates a distanceas measured from a most object side surface to a most image side surfaceat the wide position, a reference symbol S (fT) denotes a distance asmeasured from the most object side surface to the most image sidesurface at the tele position and a reference symbol L (fT) denotes atotal length of the optical system at the tele position.

[0053] The zoom optical system which has the second compositioncomprises the three lens units, and is configured for a powerdistribution among the lens units and movements of the lens units whichare substantially the same as those of the optical system which has theabove described first composition. That is, the zoom optical systemwhich has the second composition is an optical system comprising, inorder from the object side, a first lens unit G1 having positiverefractive power, a second lens unit G2 having positive refractive powerand a third lens unit G3 having negative refractive power, andconfigured for zooming from a wide position to a tele position by movingthe lens units so as to widen an airspace between the first lens unit G1and the second lens unit G2 and narrow an airspace between the secondlens unit G2 and the third lens unit G3.

[0054] Like the first composition, the above described secondcomposition also makes it possible to obtain a zoom optical system whichhas a high vari-focal ratio.

[0055] Furthermore, the first lens unit G1 of the zoom optical systemwhich has the second composition according to the present inventionconsists of two lens elements, in order from the object side, a negativemeniscus lens element which has an object side concave surface and apositive lens element which has curvature on an object side surfacehigher than that on an image side surface so that a lens system as awhole has a short total length and can favorably correct aberrations,curvature of field and astigmatism in particular.

[0056] Furthermore, the third lens unit is configured so as to comprise,in order from the object side, a biconcave lens element, a positive lenselement which has curvature on an object side convex surface higher thanthat on an image side and a negative lens element which has curvature onan object side concave surface higher than that on an image side surfaceso that aberrations, curvature of field and astigmatism in particular,can be corrected favorably.

[0057] Furthermore, the zoom optical system which has the secondcomposition is characterized by satisfying the above-mentionedconditions (2A) and (3A).

[0058] The condition (2A) defines a ratio of a variation amount of thedistance from the first surface to the final surface between the wideposition and the tele position relative to a variation amount of a focallength from the wide position to the tele position, and if a lower limitof the condition (2A) is exceeded, a correction sensitivity of the backfocal position to a positional deviation of a lens surface in thedirection of the optical axis will be high, whereby imaging performancetends to be easily lowered.

[0059] If an upper limit of the condition (2A) is exceeded, each lensunit will have a weak power, thereby making it difficult to obtain ahigh varn-focal ratio when the optical system is to be configured so asto have a short total length. When some of the lens units are to bemoved for focusing, the lens units must be moved for long distances,whereby the optical system cannot be focused on an object located at anextremely short distance.

[0060] Furthermore, the condition (3A) defines a ratio of a total lengthof the optical system at the tele position relative to a variationamount of the focal length from the wide position to the tele positionand if a lower limit of 0.8 of the condition (3A) is exceeded, sphericalaberration, coma and longitudinal chromatic aberration will be variedremarkably by zooming. If an upper limit of 1.05 is exceeded, incontrast, a telephoto ratio will be enhanced, thereby making itdifficult to shorten a total length of the optical system.

[0061] Owing to the first lens unit G1 and the third lens unit G3 whichare configured as described above, the optical system having the secondcomposition can be a compact optical system having a high vari-focalratio without defining the condition (1). When the optical system isconfigured so as to satisfy the conditions (2A) and (3A) in place of theconditions (2) and (3) in particular, the optical system can be compact,have a high vari-focal ratio, correct aberrations favorably and exhibitexcellent optical performance without satisfying the condition (4).

[0062] A zoom optical system which has a third composition according tothe present invention is an optical system comprising, in order from theobject side, a first lens unit having positive refractive power, asecond lens unit having positive refractive power and a third lens unithaving negative refractive power, and configured to change amagnification from a wide position to a tele position by moving the lensunits on the object side so as to widen an airspace between the firstlens unit and the second lens unit and narrow an airspace between thesecond lens unit and the third lens unit, wherein the third lens unithaving the negative refractive power comprises, in order from the objectside, a biconvex lens element, a positive lens element which hascurvature on an object side convex lens element higher than that on animage side surface and a negative lens element which has a curvature onan object side concave lens element higher than that on an image sidesurface, at least the airspace between the second lens unit and thethird lens unit is varied for focusing, and the zoom optical systemsatisfies the following condition (10):

[0063] (10) (β3T)²/[F(T)×0.03]<60

[0064] wherein a reference symbol β3T represents a magnification of thethird lens unit at the tele position and a reference symbol F (T)designates an F number at the tele position.

[0065] In order to obtain a high vari-focal ratio, the zoom opticalsystem having the third composition is configured for a powerdistribution among the lens units and movements of the movable lensunits for zooming which are similar to those of the optical systemshaving the above described first and second compositions. That is, thezoom optical system having the third composition comprises, in orderfrom the object side, a first lens unit G1 having positive refractivepower, a second lens unit G2 having positive refractive power and athird lens unit G3 having negative refractive power, and is configuredto perform zooming by moving the lens units on the object side so as towiden an airspace between the first lens unit G1 and the second lensunit G2 and narrow an airspace between the second lens unit G2 and thethird lens unit G3.

[0066] By configuring the above described third lens unit G3 having thenegative refractive power so as to comprise, in order from the objectside, a biconcave lens element, the positive lens element which has thecurvature on the object side convex surface higher than that on theimage side surface and the negative lens element which has the curvatureon the object side concave surface higher than that on the image sidesurface, the optical system having the third composition correctsaberrations, curvature of field and astigmatism in particular.

[0067] A lens system which consists of, in order from the object side, afirst positive lens unit G1, a second positive lens unit G2 and a thirdnegative lens unit G3 like the zoom optical system according to thepresent invention has optical performance which is lowered due to aneccentric error of the first lens unit G1 at a tele position inparticular. Accordingly, the optical system having the above describedthird composition is configured to suppress an eccentric error of thefirst lens unit G1 to a low level by varying the airspace between thesecond lens unit G2 and the third lens unit G3 for focusing, therebyshortening a moving distance of the first lens unit G1 or keeping thislens unit stationary for focusing.

[0068] Furthermore, the condition (10) defines a ratio of a square ofthe magnification β3T of the third lens unit G3 at the tele positionrelative to a depth of field. If an upper limit of 60 of this conditionis exceeded, a precision will be strict for a variation of the airspacebetween the second lens unit and the third lens unit.

[0069] Furthermore, a zoom optical system having a fourth compositionaccording to the present invention is an optical system comprising, inorder from the object side, a first lens unit G1 having positiverefractive power, a second lens unit G2 having positive refractive powerand a third lens unit having negative refractive power, and configuredto change a magnification from a wide position to a tele position bymoving the lens units on the object side so as to widen an airspacebetween the first lens unit G1 and the second lens unit G2 and narrow anairspace between the second lens unit G2 and the third lens unit G3,wherein the airspace between the second lens unit and the third lensunit is varied for focusing and the optical system satisfies thefollowing conditions (1), (4), (5) and (6):

[0070] (1) fT/fW>3.8

[0071] (4) 0<H (G1)/fTa<0.023

[0072] (5) 15<(β3T)²−(β3T)²×(β2T)²<27

[0073] (6) 0.3<f1/fTa<0.5

[0074] wherein reference symbols fW and fT represent focal lengths ofthe optical system as a whole at the wide position and the tele positionrespectively, a reference symbol fTa designates an optional focal lengthin a focal length region exceeding 3.8 times of a focal length at thewide position, a reference symbol H (G1) denotes a distance as measuredfrom a first surface to a front principal point of the first lens unit,a reference symbol f1 represents a focal length of the first lens unit,and reference symbols β2T and β3T designate magnifications of the secondlens unit and the third lens unit respectively at the tele position.

[0075] In order to have a high vari-focal ratio like the optical systemhaving the first through third compositions, the optical system havingthis fourth composition comprises, in order from the object side, afirst positive lens unit G1, a second positive lens unit G2 and a thirdnegative lens unit G3, and is configured to perform zooming from a wideposition to a tele position by moving the lens unit G1, G2 and G3 on theobject side so as to widen an airspace between the first lens unit G1and the second lens unit G2 and narrow an airspace between the secondlens unit G2 and the third lens unit G3.

[0076] Furthermore, the fourth composition is configured to performfocusing by varying at least the airspace between the second lens unitG2 and the third lens unit G3, thereby moving the first lens unit G1 fora short distance or keeping this lens unit stationary for focusing toprevent optical performance of the optical system from being lowered dueto an eccentric error of the first lens unit G1.

[0077] Furthermore, the zoom optical system having the fourthcomposition according to the present invention satisfies theabove-mentioned conditions (1), (4), (5) and (6).

[0078] The condition (1) defines a zoom ratio of the optical system andif a lower limit of the condition (1) is exceeded, it will be impossibleto configure the zoom optical system so as to have a high vari-focalratio.

[0079] The condition (4) defines a ratio of the distance H (1G) asmeasured from the first surface (most object side surface) of the firstlens unit G1 to the front principal point thereof relative to the focallength fTA in the region on a side of the tele position. If a lowerlimit of 0 of the condition (4) is exceeded, a telephoto ratio will beenhanced, whereby the optical system will have a long total length andcannot be configured compact. If an upper limit of 0.023 is exceeded, incontrast, aberrations, distortion in particular, will be overcorrected.

[0080] The condition (5) defines a correction sensitivity of an imagesurface position when the second lens unit G2 is moved in the directionof the optical axis and if a lower limit of 15 the condition (5) isexceeded, the second lens unit G2 will be moved for a long distance forfocusing, thereby forming an obstacle to shortening a shortest objectdistance. If an upper limit of 27 of the condition (5) is exceeded, incontrast, the correction sensitivity of the image surface position willbe too high and a stopping precision for the second lens unit will bestrict.

[0081] The condition (6) defines a ratio of the focal length f1 of thefirst lens unit G1 relative to the optional focal length fTa in thefocal length region exceeding 3.8 times of the focal length at the wideposition and if a lower limit of 0.3 of the condition (6) is exceeded,the first lens unit G1 will have strong refractive power and opticalperformance will be lowered remarkably due to an eccentricity of a lenselement. If an upper limit of 0.5 of the condition (6) is exceeded, incontrast, the first lens unit G1 will have weak refractive power and theoptical system will have a long total length.

[0082] It is preferable for the zoom optical system having the firstcomposition according to the present invention that the first lens unitG1 having the positive refractive power comprises, in order from theobject side, a negative meniscus lens element having a concave surfaceon the object side, and a positive lens element which has curvature onan object side convex surface higher than that on an image side surface,and that the third lens unit G3 comprises, in order from the objectside, a biconcave lens element, a positive lens element which hascurvature on an object side convex surface higher than that on an imageside surface and a negative lens element which has curvature on anobject side concave surface higher than that on an image side surface.

[0083] When the first lens unit G1 consists of two lens elements, inorder from the object side, a negative meniscus lens element having aconcave surface on the object side and a positive lens element which hascurvature on an object side surface higher than that on an image sidesurface in the above described zoom optical system according to thepresent invention as described above, it is easy to set a principalpoint of the first lens unit G1 at a location which permits shortening atotal length of the optical system and favorably correcting aberrations,distortion in particular.

[0084] For favorably correcting aberrations, curvature of field andastigmatism in particular, in the zoom optical system having the abovedescribed first or fourth composition according to the presentinvention, it is desirable to configure the third lens unit G3 so as tocomprise, in order from the object side, a biconcave lens element, apositive lens element which has curvature on an object side convexsurface higher than that on an image side surface and a negative lenselement which has curvature on an object side concave surface higherthan that on an image side surface.

[0085] Furthermore, it is desirable that the optical system having theabove described second or third composition satisfies the followingcondition (4A):

[0086] (4A) 0<H (G1)/fT<0.023

[0087] The condition (4A) defines a ratio of the distance H (G1) asmeasured from the first surface of the first lens unit G1 to the frontprincipal point of this lens unit G1 relative to the focal length of theoptical system as a whole at the tele position. If a lower limit of thecondition (4A) is exceeded, a telephoto ratio of the optical system,that is, a ratio L (T)/fT of a total length L (T) at the tele positionrelative to a focal length fT of the optical system as a whole at thetele position will be high, thereby making it impossible to configurethe optical system so as to have a short total length. If an upper limitof the condition (4A) is exceeded, aberrations, distortion inparticular, will be overcorrected.

[0088] Furthermore, it is desirable for the optical system having theabove described first, second or third composition to satisfy thefollowing condition (5):

[0089] (5) 15<(β3T)²−(β3T)²×(β2T)²<27

[0090] wherein reference symbols β2T and β3T represent magnifications ofthe second lens unit and the third lens unit respectively at the teleposition.

[0091] The above-mentioned condition (5) defines the correctionsensitivity of the image surface position when the second lens unit G2is moved in the direction of the optical axis as described above and ifa lower limit of 15 is exceeded, the second lens unit G2 will be movedfor a long distance for focusing, thereby forming an obstacle toshortening of a shortest object distance. If an upper limit of 27 isexceeded, in contrast, the correction sensitivity of the image surfacepositive will be too high, thereby posing a severer stopping precisionfor the second lens unit G2.

[0092] Furthermore, it is desirable for the optical system having theabove described first, second, third or fourth composition to satisfythe following condition (6):

[0093] (6) 0.3<f1/fT<0.5

[0094] wherein a reference symbol f1 represents a focal length of thefirst lens unit G1.

[0095] The condition (6) defines a ratio of the focal length f1 of thefirst lens unit G1 relative to the focal length fT of the optical systemas a whole at the tele position.

[0096] If a lower limit of 0.3 of the condition (6) is exceeded, thefirst lens unit will have strong refractive power, whereby opticalperformance of the optical system will be lowered remarkably due toeccentricity of a lens element. If an upper limit of 0.5 of thecondition (6) is exceeded, in contrast, the first lens unit G1 will haveweak refractive power, thereby prolonging a total length of the opticalsystem.

[0097] It is possible to correct longitudinal chromatic aberration andoffaxial chromatic aberration effectively in the optical system havingthe above described first, second, third or fourth composition byconfiguring the second lens unit G2 so as to comprise at least acemented lens component which consists of a negative lens element and apositive lens element and has negative refractive power, and a cementedlens component which consists of a negative lens element and a positivelens element and has positive refractive power.

[0098] It is desirable for the optical system having the first, second,third or fourth composition to configure the third lens unit G3 so as tocomprise an aspherical lens element on which an aspherical surface isformed by coating a thin resin film on a concave surface of a sphericallens element and configure this aspherical lens element so as to satisfythe following condition (7):

[0099] (7) 0.2<[(1/Rb−1/Ra)/(N1−N2)]Y<0.9

[0100] wherein a reference symbol Ra represents a local radius ofcurvature on the aspherical surface at a height of Y as measured from anoptical axis, that is, a distance of a normal to the aspherical surfaceat the height of Y from the optical axis as measured from the asphericalsurface to an intersection of the normal with the optical axis, areference symbol Rb designates a radius of curvature on the optical axisof the aspherical surface, and reference symbols N1 and N2 denoterefractive indices on the object side and the image side respectively ofthe aspherical surface.

[0101] When the condition (7) is satisfied, it is possible to easilyform an aspherical surface which is capable of obtaining favorableimaging performance without remarkably changing a thickness of coatedresin film.

[0102] When the thickness of the coated resin film changes remarkably onthe aspherical lens element, optical performance is degraded due totemperature and humidity variations. A remarkable change in thethickness of the coated resin film is not preferable also from aviewpoint of coagulation easiness of the resin at a manufacturing stage.

[0103] If a lower limit of the condition (7) is exceeded, an effect ofthe aspherical surface will undesirably be lost. If an upper limit ofthe condition (7) is exceeded, in contrast, aberrations will undesirablybe unbalanced in the optical system as a whole.

[0104] It is more desirable to configure the aspherical lens element soas to satisfy, in place of the condition (7), the following condition(7-1):

[0105] (7-1) −0.1<(1/Rb−1/Ra)/(N1−N2)<0.4

[0106] Furthermore, it is desirable for the optical system having theabove described first, second, third or fourth composition that anAbbe's number υ_(d) (1R) of the positive lens element disposed at a mostimage side location in the first lens unit G1 satisfies the followingcondition (8):

[0107] (8) υ_(d) (1R)>81

[0108] In case of a zoom optical system which has a short total lengthlike that according to the present invention, it is desirable to use alowly dispersive glass material for the positive lens element to bedisposed in the first lens unit G1. In other words, it is possible toreduce both longitudinal chromatic aberration and lateral chromatic byusing a glass material which satisfies the condition (8) for thepositive lens element to be disposed in the first lens unit G1.

[0109] It is desirable for the zoom optical system according to thepresent invention to configure the third lens unit G3 so as to comprisean aspherical lens element as described above. It is conceived in such acase to dispose a thin film on a lens surface and configure a surface ofthis film as an aspherical surface.

[0110] Since an image surface position of a resin film of such acomposite lens element changes due to humidity changes, it is necessaryto reduce a change of this image surface position.

[0111] In order to reduce such a change of the image surface position ofthe composite lens element due to a humidity change, it is desirable tosatisfy the following condition (9):

[0112] (9) K<0.01

[0113] wherein a reference symbol K represents a water absorption ratioof the resin which is given as K (M2−M1)/M1 when a test piece which hasa weight of M1 in a dry condition has a weight of M2 after being dippedin pure water at 23±2° C. for 23 ±1 hours.

[0114] A conventional composite lens element which uses a resin filmhaving K=0.013 cannot provide a sufficiently satisfactory change of animage surface position due to a humidity change and it is desirable thatresin has K<0.01.

[0115] It is more desirable than K<0.005.

[0116] It is possible to reduce an outside diameter of the first lensunit G1 by disposing an aperture stop S between the first lens unit G1and the second lens unit G2 in the zoom optical system according to thepresent invention. This aperture stop S is effective for lowering amanufacturing cost when an expensive glass material such as a speciallowly dispersive glass material is to be used in the first lens unit inparticular.

[0117] When the aperture stop S is disposed in the second lens unit G2of the zoom optical system according to the present invention, theaperture stop S is located nearly at a center of the optical system,thereby making it possible to favorably balance performance and preventcurvature of field from being varied by focusing the optical system froman object located at infinite distance onto an object located at anextremely short distance.

[0118] Furthermore, an outside diameter of the third lens unit G3 can bereduce by disposing the aperture stop S between the second lens unit G2and the third lens unit G3. Such disposition of the aperture stop Smakes it possible to reduce a weight of the third lens unit G3 and lowera power consumption of a driving system which moves the third lens unitG3 for focusing the optical system from the object located at theinfinite distance onto the object located at the extremely shortdistance.

[0119] Embodiments of the optical system according to the presentinvention have composition illustrated in FIGS. 1 through 12 andnumerical data which is listed below: Embodiment 1 f =39.31940˜80.13121˜164.38211, F/4.96˜F/8.10˜F/13.07 r₁ = −36.1529 d₁ =1.2000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −54.4078 d₂ = 0.2000 r₃ = 25.5545 d₃= 2.4215 n₂ = 1.49700 ν₂ = 81.54 r₄ = −133.2312 d₄ = D₁ (variable) r₅ =∞(stop) d₅ = 2.0000 r₆ = −16.9867 d₆ = 1.0000 n₃ = 1.77250 ν₃ = 49.60 r₇= 8.7422 d₇ = 3.3565 n₄ = 1.69895 ν₄ = 30.13 r₈ = −73.0473 d₈ = 0.2000r₉ = 29.0257 d₉ = 3.1240 n₅ = 1.58913 ν₅ = 61.28 r₁₀ = −19.3609(aspherical surface) d₁₀ = 0.7401 r₁₁ = −26.5554 d₁₁ = 1.0000 n₆ =1.80518 ν₆ = 25.42 r₁₂ = 26.5554 d₁₂ = 3.6355 n₇ = 1.69680 ν₇ = 55.53r₁₃ = −14.6956 d₁₃ = D₂ (variable) r₁₄ = −38.2626 (aspherical surface)d₁₄ = 0.2500 n₈ = 1.52540 ν₈ = 51.76 r₁₅ = −47.4401 d₁₅ = 1.3000 n₉ =1.77250 ν₉ = 49.60 r₁₆ = 47.4401 d₁₆ = 0.1000 r₁₇ = 33.3286 d₁₇ = 3.5615n₁₀ = 1.80518 ν₁₀ = 25.42 r₁₈ = −194.2847 d₁₈ = 4.5514 r₁₉ = −14.6422d₁₉ = 1.5000 n₁₁ = 1.69680 ν₁₁ = 55.53 r₂₀ = −490.6813 d₂₀ = D₃(variable) r₂₁ = ∞(image surface) aspherical surface coefficients (10thsurface) k = 0.1250, A₂ = 0, A₄ = 7.5359 × 10⁻⁵ A₆ = 2.0463 × 10⁻⁷, A₈ =3.2548 × 10⁻⁹ A₁₀ = −2.9785 × 10⁻¹⁰ (14th surface) k = −5.1715, A₂ = 0,A₄ = 3.2714 × 10⁻⁵ A₆ = 6.9860 × 10⁻⁸, A₈ = −9.0299 × 10⁻¹⁰ A₁₀ = 1.3124× 10⁻¹¹ f 39.31940 80.13121 164.38211 D₁ 3.68833 12.56033 19.76177 D₂12.35471 5.79428 1.33706 D₃ 8.28699 30.85166 72.96047 fW = 39.3194 , fT= 164.382 , f1 = 63, f2 = 29.4218 f3 = −17.883, β2W = 0.39372, β2T =0.50161, β3W = 1.58519, β3T = 5.20173, L(fW) = 54.4706, L(fT) = 124.2 νd(1R) = 81.54, S (fW) = 46.1836 S (fT) = 51.2394 , H (G1) = 2.24512 fT/fW= 4.18 f1/fW = 1.60, f1/fT = 0.38, f2/fT = 0.18 f3/fT = −0.11 (β3T)² −(β3T)² × (β2T)² = 20.2 [S (fT) − S (fW)]/(fT − fW) = 0.040 L (fT)/fT =0.756, L (fT)/(fT − fW) = 0.993 H (G1)/fT = 0.0137, (β3T)²/[F (T) ×0.03] = 69.0 [(1/Rb − 1/Ra)/(N1 − N2)]Y = 0.229(max) − 0.020(min) K ≈0.013 Embodiment 2 f = 39.31941˜80.13127˜154.53982,F/4.96˜F/8.10˜F/12.48 r₁ = −36.4493 d₁ = 1.2000 n₁ = 1.84666 ν₁ = 23.78r₂ = −55.5727 d₂ = 0.2000 r₃ = 25.3519 d₃ = 2.4287 n₂ = 1.49700 ν₂ =81.54 r₄ = −133.6935 d₄ = D₁ (variable) r₅ = ∞(stop) d₅ = 1.5500 r₆ =−17.4506 d₆ = 1.0000 n₃ = 1.77250 ν₃ = 49.60 r₇ = 8.8387 d₇ = 3.2826 n₄= 1.69895 ν₄ = 30.13 r₈ = −82.2223 d₈ = 0.2000 r₉ = 28.1090 d₉ = 3.3851n₅ = 1.58913 ν₅ = 61.28 r₁₀ = −19.8676 (aspherical surface) d₁₀ = 0.7812r₁₁ = −26.8571 d₁₁ = 1.0000 n₆ = 1.80518 ν₆ = 25.42 r₁₂ = 26.8571 d₁₂ =3.5757 n₇ = 1.69680 ν₇ = 55.53 r₁₃ = −14.8017 d₁₃ = D₂ (variable) r₁₄ =−38.0320 (aspherical surface) d₁₄ = 0.2500 n₈ = 1.52540 ν₈ = 51.76 r₁₅ =−47.6271 d₁₅ = 1.3000 n₉ = 1.77250 ν₉ = 49.60 r₁₆ = 47.6271 d₁₆ = 0.1000r₁₇ = 33.3180 d₁₇ = 3.5723 n₁₀ = 1.80518 ν₁₀ = 25.42 r₁₈ = −162.7512 d₁₈= 4.5439 r₁₉ = −14.2928 d₁₉ = 1.5000 n₁₁ = 1.69680 ν₁₁ = 55.53 r₂₀ =−392.1561 d₂₀ = D₃ (variable) r₂₁ = ∞(image surface) aspherical surfacecoefficients (10th surface) k = 0.0893, A₂ = 0, A₄ = 7.6179 × 10⁻⁵ A₆ =4.3848 × 10⁻⁸, A₈ = 1.2411 × 10⁻⁸ A₁₀ = −4.9402 × 10⁻¹⁰ (14th surface) k= −6.4971, A₂ = 0, A₄ = 3.3365 × 10⁻⁵ A₆ = 7.5545 × 10⁻⁹, A₈ = 1.2787 ×10⁻¹⁰ A₁₀ = 1.0155 × 10⁻¹¹ f 39.31941 80.13127 154.53982 D₁ 3.7012412.21280 19.08130 D₂ 12.41552 5.84453 1.67610 D₃ 8.28700 31.1922268.64026 fW = 39.3194, fT = 154.54, f1 = 63, f2 = 29.7966 f3 = −17.94,β2W = 0.39499, β2t = 0.49614 β3W = 1.5801, β3T = 4.9442 , L (fW) =54.2733 L (fT) = 119.267 νd_((1R) = 81.54, S (fW) = 45.9863) S (fT) =50.6269, H (G1) = 2.23928 fT/fW = 3.93 f1/fW = 1.60, f1/fT = 0.41, f2/fT= 0.19 f3/fT = −0.11 (β3T)² − (β3T)² × (β2T)² = 18.4 [S (fT) − S(fW)]/(fT − fW) = 0.040 L (fT)/fT = 0.772, L (fT)/(fT − fW) = 1.035 H(G1)/fT = 0.015. (β3T)²/[F (T) × 0.03] = 65.3 [(1/Rb − 1/Ra)/(N1 − N2)]Y= 0.234(max) − 0.020 (min) K ≈ 0.013 Embodiment 3 f =39.31940˜80.13121˜164.38211, F/4.96˜F/8.10˜F/13.07 r₁ = −36.1894 d₁ =1.2000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −54.2948 d₂ = 0.2000 r₃ = 25.5904d_(3 = 2.4505) n₂ = 1.49700 ν₂ = 81.54 r₄ = −130.0396 d₄ = D₁ (variable)r₅ = ∞(stop) d₅ = 2.0000 r₆ = −16.8396 d₆ = 1.0000 n₃ = 1.77250 ν₃ 49.60r₇ = 8.7377 d₇ = 3.3498 n₄ = 1.69895 ν₄ = 30.13 r₈ = −74.7437 d₈ =0.2000 r₉ = 29.0957 d₉ = 3.1237 n₅ = 1.58913 ν₅ = 61.28 r₁₀ = −19.2788(aspherical surface) d₁₀ = 0.7122 r₁₁ = −26.7824 d₁₁ = 1.0000 n₆ =1.80518 ν₆ = 25.42 r₁₂ = 26.7824 d₁₂ = 3.6300 n₇ = 1.69680 ν₇ = 55.53r₁₃ = −14.7035 d₁₃ = D₂ (variable) r₁₄ = −38.5269 (aspherical surface)d₁₄ = 0.2500 n₈ = 1.53416 ν₈ = 40.99 r₁₅ = −47.6601 d₁₅ = 1.3000 n₉ =1.77250 ν₉ = 49.60 r₁₆ = 47.6601 d₁₆ = 0.1000 r₁₇ = 33.7700 d₁₇ = 3.5590n₁₀ = 1.80518 ν₁₀ = 25.42 r₁₈ = −183.6194 d₁₈ = 4.5556 r₁₉ = −14.6445d₁₉ = 1.5000 n₁₁ = 1.69680 ν₁₁ = 55.53 r₂₀ = −471.5265 d₂₀ = D₃(variable) r₂₁ = ∞(image surface) aspherical surface coefficients (10thsurface) k = −0.0859, A₂ = 0, A₄ = 7.1654 × 10⁻⁵ A₆ = 2.9034 × 10⁻⁷, A₈= −2.2409 × 10⁻⁹ A₁₀ = −1.9366 × 10⁻¹⁰ (14th surface) k = −5.0472, A₂ =0, A₄ = 3.2262 × 10⁻⁵ A₆ = 9.5888 × 10⁻⁸, A₈ = −1.3521 × 10⁻⁹ A₁₀ =1.5070 × 10⁻¹¹ f 39.31940 80.13121 164.38211 D₁ 3.67961 12.5329919.66716 D₂ 12.41653 5.81695 1.33350 D₃ 8.28699 30.86803 73.06844 fW =39.3194, fT = 164.382, f1 = 62.535, f2 = 29.493 f3 = −17.933, β2W =0.39701, β2T = 0.50588, β3W = 1.58373, β3T = 5.19614, L (fW) = 54.5139,L (fT) = 124.2 νd (1R) = 81.54, S (fW) = 46.2269 S (fT) = 51.1315, H(G1) = 2.24678 fT/fW = 4.18 f1/fW = 1.59, f1/fT = 0.38, f2/fT = 0.18f3/fT = −0.11 (β3T)² − (β3T)² × (β2T)² = 20.1 [S (fT) − S (fW)]/(fT −fW) = 0.039 L (fT)/fT = 0.756, L (fT)/(fT − fW) = 0.993 H (G1)/fT =0.0137, (β3T)²/[F (T) × 0.03] = 68.9 [(1/Rb − 1/Ra)/(N1 − N2)]Y =0.226(max) − 0.019(min) K ≈ 0.004 Embodiment 4 f =39.31940˜80.13121˜193.30266, F/4.96˜F/8.10˜F/14.76 r₁ = −36.3477 d₁ =1.2000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −54.7150 d₂ = 0.2000 r₃ = 25.5347 d₃= 2.4505 n₂ = 1.49700 ν₂ = 81.54 r₄ = −127.2069 d₄ = D₁ (variable) r₅ =∞(stop) d₅ = 2.0000 r₆ = −16.7002 d₆ = 1.0000 n₃ = 1.77250 ν₃ = 49.60 r₇= 8.7781 d_(7 = 3.3498) n₄ = 1.69895 ν₄ = 30.13 r₈ = −72.9099 d₈ =0.2000 r₉ = 29.3486 d₉ = 3.1237 n₅ = 1.58913 ν₅ = 61.28 r₁₀ = −19.2291(aspherical surface) d₁₀ = 0.7122 r₁₁ = −27.2785 d₁₁ = 1.0000 n₆ =1.80518 ν₆ = 25.42 r₁₂ = 26.3908 d₁₂ = 3.6300 n₇ = 1.69680 ν₇ = 55.53r₁₃ = −14.7850 d₁₃ = D₂ (variable) r₁₄ = −39.6276 (aspherical surface)d₁₄ = 0.2500 n₈ = 1.53416 ν₈ = 40.99 r₁₅ = −49.3489 d₁₅ = 1.3000 n₉ =1.77250 ν₉ = 49.60 r₁₆ = 44.1627 d₁₆ = 0.1000 r₁₇ = 33.3027 d₁₇ = 3.5590n₁₀ = 1.80518 ν₁₀ = 25.42 r₁₈ = −189.4038 d₁₈ = 4.5556 r₁₉ = −14.5720d₁₉ = 1.5000 n₁₁ = 1.69680 ν₁₁ = 55.53 r₂₀ = −317.8457 d₂₀ = D₃(variable) r₂₁ = ∞(image surface) aspherical surface coefficients (10thsurface) k = −0.0859, A₂ = 0, A₄ = 7.1654 × 10⁻⁵ A₆ = 2.9034 × 10⁻⁷, A₈= −2.2409 × 10⁻⁹ A₁₀ = −1.9366 × 10⁻¹⁰ (14th surface) k = −5.2953, A₂ =0, A₄ = 3.2462 × 10⁻⁵ A₆ = 1.2152 × 10⁻⁷, A₈ = −1.8474 × 10⁻⁹ A₁₀ =1.7629 × 10⁻¹¹ f 39.31940 80.13121 193.30266 D₁ 3.67904 12.4834120.98000 D₂ 12.35828 5.78330 0.50000 D₃ 8.28699 30.87775 86.83828 fW =39.3194, fT = 193.303, f1 = 62.1246, f2 = 29.4063 f3 = −17.892, β2W =0.39843, β2T = 0.52043 β3W = 1.58851, β3T = 5.9788, L (fW) = 54.4551 L(fT) = 138.449 νd (1R) = 81.54, S (fW) = 46.1681 S (fT) = 51.6108, H(G1) = 2.24238 fT/fW = 4.92 f1/fW = 1.58, f1/fT = 0.32, f2/fT = 0.15f3/fT = −0.09 (β3T)² − (β3T)² × (β2T)² = 26.1 [S (fT) − S (fW)]/(fT −fW) = 0.035 L (fT)/fT = 0.716, L (fT)/(fT − fW) = 0.899 H (G1)/fT =0.012, (β3T)²/[F (T) × 0.03] = 80.7 [(1/Rb − 1/Ra)/(N1 − N2)]Y =0.213(max) − 0.019(min) K ≈ 0.004 Embodiment 5 f =39.29851˜80.05797˜174.70221 F/4.97˜F/7.80˜F/13.69 r₁ = 36.1261 d₁ =1.2000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −54.4475 d₂ = 0.2000 r₃ = 25.5172 d₃=2.4500 n₂ = 1.49700 ν₂ = 81.54 r₄ = −133.2284 d₄ = D₁ (variable) r₅ =∞(stop) d₅ = 2.0000 r₆ = −16.9532 d₆ = 1.0000 n₃ = 1.77250 ν₃ = 49.60 r₇= 8.7541 d₇ = 3.3500 n₄ = 1.69895 ν₄ = 30.13 r₈ = −73.0913 d₈ = 0.2000r₉ = 28.8312 d₉ = 3.1200 n₅ = 1.58913 ν₅ = 61.28 r₁₀ = −19.3441(aspherical surface) d₁₀ = 0.7100 r₁₁ = −26.5172 d₁₁ = 1.0000 n₆ =1.80518 ν₆ = 25.42 r₁₂ = 26.5172 d₁₂ = 3.6300 n₇ = 1.69680 ν₇ = 55.53r₁₃ = −14.7051 d₁₃ = D₂ (variable) r₁₄ = −38.0113 (aspherical surface)d₁₄ = 0.2500 n₈ = 1.50573 ν₈ = 56.19 r₁₅ = −47.4953 d₁₅ = 1.3000 n₉ =1.77250 ν₉ = 49.60 r₁₆ = 47.4953 d₁₆ = 0.1000 r₁₇ = 33.3930 d₁₇ = 3.5600n₁₀ = 1.80518 ν₁₀ = 25.42 r₁₈ = −194.3824 d₁₈ = 4.5600 r₁₉ = −14.6522d₁₉ = 1.5000 n₁₁ = 1.69680 ν₁₁ = 55.53 r₂₀ = −493.1845 d₂₀ = D₃(variable) r₂₁ = ∞(image surface) aspherical surface coefficients (10thsurface) k = −0.0859, A₂ = 0, A₄ = 7.1654 × 10⁻⁵ A₆ = 2.9034 × 10⁻⁷, A₈= −2.2409 × 10⁻⁹ A₁₀ = −1.9366 × 10⁻¹⁰ (14th surface) k = −3.2629, A₂ =0, A₄ = 3.8379 × 10⁻⁵ A₆ = 7.9877 × 10⁻⁸, A₈ = −1.1213 × 10⁻⁹ A₁₀ =1.3947 × 10⁻¹¹ f 39.29851 80.05797 174.70221 D₁ 3.69830 12.5703020.38600 D₂ 12.35587 5.79424 1.00580 D₃ 8.27239 30.81038 77.78114 fW =39.2985, fT = 174.702, f1 = 63.0009, f2 = 29.4247 f3 = −17.886, β2W =0.39371, β2T = 0.5069, β3W = 1.58434, β3T = 5.47057, L (fW) = 54.4566, L(fT) = 129.303 νd (1R) = 81.54, S (fW) = 46.1842 S (fT) = 51.5218, H(G1) = 2.25057 fT/fW = 4.45 f1/fW = 1.60, f1/fT = 0.36, f2/fT = 0.17f3/fT = −0.10 (β3T)² − (β3T)² × (β2T)² = 22.23 [S (fT) − S (fW)]/(fT −fW) = 0.039 L (fT)/fT = 0.740, L (fT)/(fT − fW) = 0.955 H (G1)/fT =0.0129 (β3T)²/[F (T) × 0.03] = 72.8 [(1/Rb − 1/Ra)/(N1 − N2)] Y =0.230(max) − 0.020(min) K ≈ 0.004 Embodiment 6 f =39.00131˜77.99475˜154.97196, F/5.07˜F/7.93˜F/12.40 r₁ = −55.2820 d₁ =1.2000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −120.9191 d₂ = 0.2000 r₃ = 22.8989d₃ = 2.6969 n₂ = 1.49700 ν₂ = 81.54 r₄ = −293.2573 d₄ = D₁ (variable) r₅= −18.4950 d₅ = 1.2226 n₃ = 1.80440 ν₃ = 39.59 r₆ = 12.9349 d₆ = 3.6678n₄ = 1.75520 ν₄ = 27.51 r₇ = −50.3791 d₇ = 0.5546 r₈ = ∞(stop) d₈ =2.8591 r₉ = 16.9870 d₉ = 2.6078 n₅ = 1.80809 ν₅ = = 22.76 r₁₀ = 10.5546d₁₀ = 3.9730 n₆ = 1.51633 ν₆ = 64.14 r₁₁ = −16.4665 (aspherical surface)d₁₁ = D₂ (variable) r₁₂ = −30.5029 (aspherical surface) d₁₂ = 0.2500 n₇= 1.52288 ν₇ = 52.50 r₁₃ = −39.6951 d₁₃ = 1.0000 n₈ = 1.77250 ν₈ = =49.60 r₁₄ = 235.6280 d₁₄ = 0.2000 r₁₅ = 47.5727 d₁₅ = 3.0797 n₉ =1.80809 ν₉ = 22.76 r₁₆ = −115.6313 d₁₆ = 3.9290 r₁₇ = −15.0820 d₁₇ =1.5000 n₁₀ = 1.77250 ν₁₀ = 49.60 r₁₈ = −8611.4904 d₁₈ = D₃ (variable)r₁₉ = ∞(image surface) aspherical surface coefficients (11th surface) k= −1.0134, A₂ = 0, A₄ = 3.5513 × 10⁻⁵ A₆ = −3.5589 × 10⁻⁷, A₈ = 1.3077 ×10⁻⁸ A₁₀ = −2.3711 × 10⁻¹⁰ (12th surface) k = −1.1562, A₂ = 0, A₄ =5.3599 × 10⁻⁵ A₆ = 1.8661 × 10⁻⁷, A₈ = −1.5844 × 10⁻⁹ A₁₀ = 1.0255 ×10⁻¹¹ f 39.00131 77.99475 154.97196 D₁ 2.42919 12.47865 17.14445 D₂13.07736 6.48724 2.50000 D₃ 8.50048 29.49424 71.39986 fW = 39.0013, fT =154.972, f1 = 65, f2 = 30.3329 f3 = −17.967, β2W = 0.38308, β2T =0.47052 β3W = 1.56632, β3T = 5.06716, L (fW) = 52.9476, L (fT) = 119.985νd (1R) = 81.54, S (fW) = 44.4471 S (fT) = 48.5851, H (G1) = 1.78077fT/fW = 3.97 f1/fW = 1.67, f1/fT = 0.42, f2/fT = 0.20 f3/fT = −0.12(β3T)² − (β3T)² × (β2T)² = 20.0 [S (fT) − S (fW)]/(fT − fW) = 0.036 L(fT)/fT = 0.774, L (fT) (fT − fW) = 1.035 H (G1)/fT = 0.0115, (β3T)²/[F(T) × 0.03] = 69.0 [1/Rb − 1/Ra)/(N1 − N2)]Y = 0.204(max) − 0.032 (min)K ≈ 0.013 Embodiment 7 f = 39.00006˜78.00015˜155.00050,F/5.07˜F/7.93˜F/12.40 r₁ = −41.7856 d₁ = 1.2000 n₁ = 1.84666 ν₁ = 23.78r₂ = −71.0649 d₂ = 0.2000 r₃ = 27.0469 d₃ = 3.0355 n₂ = 1.49700 ν₂ =81.54 r₄ = −100.2000 d₄ = D₁ (variable) r₅ = −19.5893 d₅ = 1.2226 n₃ =1.83400 ν₃ = 37.16 r₆ = 10.2509 d₆ = 3.8546 n₄ = 1.74077 ν₄ = 27.79 r₇ =−34.7172 d₇ = 0.5546 r₈ = ∞(stop) d₈ = 3.7692 r₉ = 17.7730 d₉ = 2.3607n₅ = 1.80809 ν₅ = 22.76 r₁₀ = 11.2606 d₁₀ = 4.4446 n₆ = 1.48749 ν₆ =70.23 r₁₁ = −15.4109 (aspherical surface) d₁₁ = D₂ (variable) r₁₂ =−46.7644 (aspherical surface) d₁₂ = 0.2500 n₇ = 1.52288 ν₇ = 52.50 r₁₃ =−84.1095 d₁₃ = 1.0000 n₈ = 1.80400 ν₈ = 46.57 r₁₄ = 74.4998 d₁₄ = 0.2000r₁₅ = 43.7443 d₁₅ = 2.7938 n₉ = 1.80809 ν₉ = 22.76 r₁₆ = −280.1664 d₁₆ =4.7710 r₁₇ = −12.8051 d₁₇ = 1.5000 n₁₀ = 1.72916 ν₁₀ = 54.68 r₁₈ =−152.0771 d₁₈ = D₃ (variable) r₁₉ = ∞(image surface) aspherical surfacecoefficients (11th surface) k = −0.6080, A₂ = 0, A₄ = 2.6727 × 10⁻⁵ A₆ =−2.0459 × 10⁻⁷, A₈ = 4.8924 × 10⁻⁹ A₁₀ = −1.7009 × 10⁻¹⁰ (12th surface)k = −3.9144, A₂ = 0, A₄ = 5.6210 × 10⁻⁵ A₆ = 1.9143 × 10⁻⁷, A₈ = −1.5570× 10⁻⁹ A₁₀ = 1.8313 × 10⁻¹¹ f 39.00006 78.00015 155.00050 D₁ 2.3971313.38809 17.71289 D₂ 12.68411 6.32098 2.50000 D₃ 8.50003 28.1782468.63072 fW = 39.0001, fT = 155.001, f1 = 65, f2 = 29.2361 f3 = −17.286,β2W = 0.37747, β2T = 0.47051, β3W = 1.58954, β3T = 5.06819, L (fW) =54.7379, L (fT) = 120 νd (1R) = 81.54, S (fW) = 46.2379 S (fT) = 51.3695, H (G1) = 2.42839 fT/fW = 3.97 f1/fW = 1.67, f1/fT = 0.42, f2/fT = 0.19f3/fT = −0.11 (β3T)² − (β3T)² × (β2T)² = 20.0 [S (fT) − S (fW)]/(fT −fW) = 0.044 L (fT)/fT = 0.774, L (fT)/(fT − fW) = 1.034 H (G1)/fT =0.0157 (β3T)²/[F (T) × 0.03] = 69.0 [(1/Rb − 1/Ra)/(N1 − N2)]Y =0.245(max) − 0.043 min K ≈ 0.013 Embodiment 8 f =39.34207˜78.02837˜154.35649, F/4.93˜F/7.49˜F/12.38 r₁ = −44.5650 d₁ =1.5000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −66.0577 d₂ = 0.1500 r₃ = 24.1165 d₃= 3.8000 n₂ = 1.49700 ν₂ = 81.54 r₄ = 237.8975 d₄ = D₁ (variable) r₅ =−20.7950 d₅ = 1.4500 n₃ = 1.83400 ν₃ = 37.16 r₆ = 11.1186 d₆ = 3.5500 n₄= 1.72825 ν₄ = 28.46 r₇ = 160.8286 d₇ = 0.1200 r₈ = 19.6614 d₈ = 3.6336n₅ = 1.80809 ν₅ = 22.76 r₉ = 15.0183 d₉ = 3.0000 n₆ = 1.51742 ν₆ = 52.43r₁₀ = −64.0395 d₁₀ = 0.1500 r₁₁ = 32.3241 d₁₁ = 2.4500 n₇ = 1.51633 ν₇ == 64.14 r₁₂ = −19.3761 (aspherical surface) d₁₂ = D₂ (variable) r₁₃ =∞(stop) d₁₃ = D₃ (variable) r₁₄ = −18.9165 (aspherical surface) d₁₄ =0.1500 n₈ = 1.52288 ν₈ = 52.50 r₁₅ = −26.9708 d₁₅ = 2.3000 n₉ = 1.80809ν₉ = 22.76 r₁₆ = −17.9565 d₁₆ = 3.2228 r₁₇ = −9.7000 d₁₇ = 1.6000 n₁₀ =1.72916 ν₁₀ = 54.68 r₁₈ = −59.2171 d₁₈ = D₄ (variable) r₁₉ = ∞(imagesurface) aspherical surface coefficients (12th surface) k = −0.7229, A₂= 0, A₄ = 4.2016 × 10⁻⁵ A₆ = −6.4534 × 10⁻¹⁰, A₈ = 5.4085 × 10⁻¹¹ A₁₀ =5.8453 × 10⁻¹¹ (14th surface) k = −10.9706, A₂ = 0, A₄ = −8.7105 × 10⁻⁵A₆ = 2.7106 × 10⁻⁶, A₈ = −1.6444 × 10⁻⁸ A₁₀ = 1.2744 × 10⁻¹⁰ f 39.3420778.02837 154.35649 D₁ 3.42320 12.58945 16.38676 D₂ 0.50000 0.500000.50000 D₃ 14.49499 7.46666 3.29506 D₄ 8.38971 29.23621 71.59514 fW =39.3421, fT = 154.356, f1 = 58.8059, f2 = 31.8882 f3 = −18.38, β2W =0.43406, β2T = 0.52706, β3W = 1.54131, β3T = 4.98016, L (fW) = 53.8842 L(fT) = 118.853 νd (1R) = 81.54, S (fW) = 45.4945 S (fT) = 47.2582, H(G1)= 2.19696 fT/fW = 3.92 f1/fW = 1.49, f1/fT = 0.38, f2/fT = 0.21 f3/fT =−0.12 (β3T)² − (β3T)² × (β2T)² = 17.91 [S (fT) − S (fW)]/(fT − fW) =0.015 L (fT)/fT = 0.770, L (fT)/(fT − fW) = 1.033 H (G1)/fT = 0.0142(β3T)²/[F (T) × 0.03] = 66.8 [(1/Rb − 1/Ra)/(N1 − N2)]Y = 0.319(max) −0.067(min) K ≈ 0.013 Embodiment 9 f = 39.33845˜85.89193˜192.41503,F/4.79˜F/8.07˜F/13.90 r₁ = −40.0753 d₁ = 1.5000 n₁ = 1.84666 ν₁ = 23.78r₂ = −59.5371 d₂ = 0.1500 r₃ = 30.1811 d₃ = 3.7000 n₂ = 1.49700 ν₂ =81.54 r₄ = −117.0178 d₄ = D₁ (variable) r₅ = −22.3137 d₅ = 1.4500 n₃ =1.83400 ν₃ = 37.16 r₆ = 13.4338 d₆ = 3.2500 n₄ = 1.72825 ν₄ = 28.46 r₇ =−108.7335 d₇ = 0.1500 r₈ = 33.7625 d₈ = 6.9858 n₅ = 1.80809 ν₅ = 22.76r₉ = 21.1104 d₉ = 2.9000 n₆ = 1.51742 ν₆ = 52.43 r₁₀ = −54.8767 d₁₀ =0.1500 r₁₁ = 39.6423 d₁₁ = 2.4500 n₇ = 1.51633 ν₇ = = 64.14 r₁₂ =−21.4789 (aspherical surface) d₁₂ = D₂ (variable) r₁₃ = ∞(stop) d₁₃ = D₃(variable) r₁₄ = −33.4820 (aspherical surface) d₁₄ = 0.1500 n₈ = 1.52288ν₈ = 52.50 r₁₅ = −56.6945 d₁₅ = 1.4500 n₉ = 1.80100 ν₉ = 34.97 r₁₆ =80.5137 d₁₆ = 0.2900 r₁₇ = 40.9960 d₁₇ = 3.1032 n₁₀ = 1.80518 ν₁₀ =25.42 r₁₈ = −65.7107 d₁₈ = 4.8609 r₁₉ = −12.0731 d₁₉ = 1.6800 n₁₁ =1.77250 ν₁₁ = 49.60 r₂₀ = −84.4506 d₂₀ = D₄ (variable) r₂₁ = ∞(imagesurface) aspherical surface coefficients (12th surface) k = −0.8485 , A₂= 0, A₄ = 7.4293 × 10⁻⁶ A₆ = 1.2276 × 10⁻⁷, A₈ = −1.9410 × 10⁻¹¹ A₁₀ =−2.0467 × 10⁻¹¹ (14th surface) k = −18.6612, A₂ = 0, A₄ = 3.1184 × 10⁻⁶A₆ = 5.1849 × 10⁻⁷, A₈ = 3.1155 × 10⁻⁹ A₁₀ = −7.6338 × 10⁻¹² f 39.3384585.89193 192.41503 D₁ 3.60000 12.44329 20.17378 D₂ 0.50000 0.500000.50000 D₃ 15.43402 7.47062 2.41555 D₄ 6.02914 31.28139 83.65253 fW =39.3384, fT = 192.415, f1 = 69.8198, f2 = 34.0092 f3 = −18.581, β2W =0.39714, β2T = 0.49245, β3W = 1.4187 β3T = 5.59621, L (fW) = 59.7831 , L(fT) = 140.962 νd (1R) = 81.54, S (fW) = 53.7539 S (fT) = 57.3093, H(G1) = 2.90859 fT/fW = 4.89 f1/fW = 1.77, f1/fT = 0.36, f2/fT = 0.18f3/fT = −0.10 (β3T)² − (β3T)² × (β2T)² = 23.7 [S (fT) − S (fW)]/(fT −fW) = 0.023 L (fT)/fT = 0.733, L (fT)/(fT − fW) = 0.921 H (G1)/fT =0.0151, (β3T)²/[F (T) × 0.03] = 75.1 [(1/Rb − 1/Ra)/(N1 − N2)]Y =0.278(max) − 0.060 (min) K ≈ 0.013 Embodiment 10 f =39.29010˜80.99964˜164.90506 F/4.95˜F/7.56˜F/12.88 r₁ = −46.4813 d₁ =1.5000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −72.0162 d₂ = 0.1500 r₃ = 23.9772 d₃= 3.8000 n₂ = 1.49700 ν₂ = 81.54 r₄ = −290.6726 d₄ = D₁ (variable) r₅ =−21.2421 d₅ = 1.4500 n₃ = 1.83400 ν₃ = 37.16 r₆ = 11.5296 d₆ = 3.5500 n₄= 1.72825 ν₄ = 28.46 r₇ = 96.4682 d₇ = 0.1200 r₈ = 19.4334 d₈ = 3.8916n₅ = 1.80809 ν₅ = 22.76 r₉ = 15.9101 d₉ = 3.0000 n₆ = 1.51742 ν₆ = 52.43r₁₀ = −63.2316 d₁₀ = 0.1500 r₁₁ = 28.6858 d₁₁ = 2.4500 n₇ = 1.51633 ν₇ =64.14 r₁₂ = −20.4382 (aspherical surface) d₁₂ = D₂ (variable) r₁₃ =∞(stop) d₁₃ = D₃ (variable) r₁₄ = −19.3623 (aspherical surface) d₁₄ =0.1500 n₈ = 1.52288 ν₈ = 52.50 r₁₅ = −28.3069 d₁₅ = 2.3000 n₉ = 1.80809ν₉ = 22.76 r₁₆ = −18.3891 d₁₆ = 3.2463 r₁₇ = −9.7000 d₁₇ = 1.6000 n₁₀ =1.72916 ν₁ = 54.68 r₁₈ = −59.3087 d₁₈ = D₄ (variable) r₁₉ = ∞(imagesurface) aspherical surface coefficients (12th surface) k = −0.7080, A₂= 0, A₄ = 4.9153 × 10⁻⁵ A₆ = −1.4374 × 10⁻⁸, A₈ = 8.6252 × 10⁻¹¹ A₁₀ =9.4428 × 10⁻¹¹ (14th surface) k = −10.9468, A₂ = 0, A₄ = −7.3774 × 10⁻⁵A₆ = 2.4231 × 10⁻⁶, A₈ = −1.4086 × 10⁻⁸ A₁₀ = 1.2143 × 10⁻¹⁰ f 39.2901080.99964 164.90506 D₁ 3.42140 12.38821 16.45077 D₂ 0.50000 0.500000.50000 D₃ 14.55169 7.39524 3.27562 D₄ 8.39751 31.47837 78.28210 fW =39.2901, fT = 164.905, f1 = 60.8189, f2 = 31.4554 f3 = −18.392, β2W =0.41955, β2T = 0.5078 β3W = 1.53977, β3T = 5.33948 , L (fW) = 54.2285 L(fT) = 125.866 νd (1R) = 81.54, S (fW) = 45.831 S (fT) = 47.5843, H (G1)= 2.14819 fT/fW = 4.20 f1/fW = 1.55, f1/fT = 0.37, f2/fT = 0.19 f3/fT =−0.11 (β3T)² − (β3T)² × (β2T)² = 21.2 [S (fT) − S (fW)]/(fT − fW) =0.014 L (fT)/fT = 0.763, L (fT)/(fT − fW) = 1.002 H (G)/fT = 0.0130,(β3T)²/[F (T) × 0.03] = 73.86 [(1/Rb − 1/Ra)/(N1 − N2)]Y = 0.305(max) −0.071(min) K ≈ 0.013 Embodiment 11 f = 39.31940˜80.13121˜137.03257,F/4.96˜F/8.10˜F/11.60 r₁ = −36.1260 d₁ = 1.2000 n₁ = 1.84666 ν₁ = 23.78r₂ = −54.4470 d₂ = 0.2000 r₃ = 25.5170 d₃ = 2.4505 n₂ = 1.49700 ν₂ =81.54 r₄ = −133.2280 d₄ = D₁ (variable) r₅ = ∞(stop) d₅ = 2.0000 r₆ =−16.9530 d_(6 = 1.0000) n₃ = 1.77250 ν₃ = 49.60 r₇ = 8.7540 d₇ = 3.3498n₄ = 1.69895 ν₄ = 30.13 r₈ = −73.0910 d₈ = 0.2000 r₉ = 28.8310 d₉ =3.1237 n₅ = 1.58913 ν₅ = 61.28 r₁₀ = −19.3440 (aspherical surface) d₁₀ =0.7122 r₁₁ = −26.5170 d₁₁ = 1.0000 n₆ = 1.80518 ν₆ = 25.42 r₁₂ = 26.5170d₁₂ = 3.6300 n₇ = 1.69680 ν₇ = 55.53 r₁₃ = −14.7050 d₁₃ = D₂ (variable)r₁₄ = −38.4185 (aspherical surface) d₁₄ = 0.2500 n₈ = 1.53416 ν₈ = 40.99r₁₅ = −47.4950 d₁₅ = 1.3000 n₉ = 1.77250 ν₉ = 49.60 r₁₆ = 47.4950 d₁₆ =0.1000 r₁₇ = 33.3930 d₁₇ = 3.5590 n₁₀ = 1.80518 ν₁₀ = 25.42 r₁₈ =−194.3820 d₁₈ = 4.5556 r₁₉ = −14.6520 d₁₉ = 1.5000 n₁₁ = 1.69680 ν₁₁ =55.53 r₂₀ = −493.1840 d₂₀ = D₃ (variable) r₂₁ = ∞(image surface)aspherical surface coefficients (10th surface) k = −0.0859, A₂ = 0, A₄ =7.1654 × 10⁻⁵ A₆ = 2.9034 × 10⁻⁷, A₈ = −2.2409 × 10⁻⁹ A₁₀ = −1.9366 ×10⁻¹⁰ (14th surface) k = −4.9241, A₂ = 0, A₄ = 3.2424 × 10⁻⁵ A₆ = 8.8177× 10⁻⁸, A₈ = −1.2634 × 10⁻⁹ A₁₀ = 1.4913 × 10⁻¹¹ f 39.31940 80.13121137.03257 D₁ 3.69700 12.56900 18.74777 D₂ 12.35743 5.79601 2.20674 D₃8.28699 30.85587 58.84557 fW = 39.319, fT = 137.03, f1 = 63, f2 = 29.424f3 = −17.89, β2W = 0.3937, β2T = 0.493, β3W = 1.5852, β3T = 4.4119, L(fW) = 54.472, L (fT) = 109.93 νd (1R) = 81.54, S (fW) = 46.185 S (fT) =51.085, H (G1) = 2.2506 fT/fW = 3.49 f1/fW = 1.60 , f1/fT = 0.46, f2/fT= 0.21 f3/fT = −0.13 (β3T)² − (β3T)² × (β2T)² = 14.7 [S (fT) − S(fW)]/(fT − fW) = 0.050 L (fT)/fT = 0.802, L (fT)/(fT − fW) = 1.125 H(G1)/fT = 0.0164 (β3T)²/[F (T) × 0.03] = 55.9 [(1/Rb − 1/Ra)/(N1 − N2)]Y= 0.226(max) − 0.020(min) K ≈ 0.004 Embodiment 12 f =39.34121˜77.94504˜154.51615, F/4.84˜F/7.51˜F/12.61 r₁ = −36.4108 d₁ =1.5000 n₁ = 1.84666 ν₁ = 23.78 r₂ = −56.5926 d₂ = 0.1500 r₃ = 29.0859d₁₃ = 3.8000 n₂ = 1.48749 ν₂ = 70.23 r₄ = −77.9135 d₄ = D₁ (variable) r₅= −20.0548 d₅ = 1.500 n₃ = 1.83400 ν₃ = 37.16 r₆ = 14.2756 d₆ = 2.8500n₄ = 1.72825 ν₄ = 28.46 r₇ = −158.9545 d₇ = 0.1500 r₈ = 22.6216 d₈ =5.6315 n₅ = 1.80809 ν₅ = 22.76 r₉ = 15.9458 d₉ = 2.9000 n₆ = 1.51742 ν₆= 52.43 r₁₀ = −29.4439 d₁₀ = 0.1500 r₁₁ = 55.4112 d₁₁ = 2.2000 n₇ =1.51633 ν₇ = 64.14 r₁₂ = −26.3943 (aspherical surface) d₁₂ = D₂(variable) r₁₃ = ∞(stop) d₁₃ = D₃ (variable) r₁₄ = −47.0444 (asphericalsurface) d₁₄ = 1.6000 n₈ = 1.80100 ν₈ = 34.97 r₁₅ = 63.2540 d₁₅ = 0.2900r₁₆ = 46.5210 d₁₆ = 2.8000 n₉ = 1.80809 ν₉ = 22.76 r₁₇ = −103.2100 d₁₇ =4.7038 r₁₈ = −11.1087 d₁₈ = 1.6800 n₁₀ = 1.69680 ν₁ = 55.53 r₁₉ =−55.0157 d₁₉ = D₄ (variable) r₂₀ = ∞(image surface) aspherical surfacecoefficients (12th surface) k = −0.7930, A₂ = 0, A₄ = 2.2146 × 10⁻⁵ A₆ =1.7367 × 10⁻⁷, A₈ = −3.1388 × 10⁻⁹ A₁₀ = −4.0872 × 10⁻¹¹ (14th surface)k = −18.4524, A₂ = 0, A₄ = 2.4464 × 10⁻⁵ A₆ = 1.3026 × 10⁻⁷, A₈ = 4.4800× 10⁻⁹ A₁₀ = −2.6832 × 10⁻¹¹ f 39.34121 77.94504 154.51615 D₁ 2.5000012.16724 17.11258 D₂ 0.50000 0.50000 0.50000 D₃ 13.65201 6.85601 2.68979D₄ 6.77765 27.02242 67.09830 fW = 39.341, fT = 154.52, f1 = 65.255, f2 =33.364 f3 = −17.8, β2W = 0.3989, β2T = 0.4833 β3W = 1.5115, β3T =4.8995, L (fW) = 55.335, L (fT) = 119.31 νd (1R) = 70.23, S (fW) =48.557 S (fT) = 52.208, H (G1) = 3.2491 fT/fW = 3.93 f1/fW = 1.66, f1/fT= 0.42, f2/fT = 0.22 f3/fT = −0.12 (β3T)² − (β3T)² × (β2T)² = 18.4 [S(fT) − S (fW)]/(fT − fW) = 0.032 L (fT)/fT = 0.7721, L (fT)/(fT − fW) =1.036 H (G1)/fT = 0.021, (β3T)²/F (T) × 0.03 = 63.4

[0120] wherein reference symbols r₁, r₂, . . . represent radii ofcurvature on respective lens surfaces, reference symbols d₁, d₂, . . .designate thicknesses of respective lens elements and airspaces reservedtherebetween, reference symbols n₁, n₂, . . . denote refractive indicesof the respective lens elements, and reference symbols ), υ₁, υ₂. . .represent Abbe's number of the respective lens elements. In additionlengths such as r₁, r₂, . . . d₁, d₂, . . . in the numerical data areexpressed in a unit of mm.

[0121] The first embodiment has a composition illustrated in FIG. 1 andcomprises a first positive lens unit G1, a second positive lens unit G2and a third negative lens unit G3.

[0122] The first lens unit G1 of this optical system consists of anegative meniscus lens element (r₁ to r₂) having a concave surface onthe object side and a positive lens element (r₃ to r₄) which hascurvature on an object side surface higher than that on an image sidesurface.

[0123] The second lens unit G2 consists of a cemented lens component (r₆through r₈) consisting of a negative lens element and a positive lenselement, a positive lens element (r₉ to r₁₀), and a cemented lenscomponent (r₁, through r₁₃) consisting of a negative lens element and apositive lens element.

[0124] Furthermore, the third lens unit G3 consists of a biconcave lenselement (r₁₅ to r₁₆), a positive lens element (r₁₇ to r₁₈) which hascurvature on an object side convex surface higher than that on an imageside surface and a negative lens element (r₁₉ to r₂₀) which hascurvature on an object side concave surface higher than that on an imageside surface.

[0125] In the first embodiment, the most object side biconcave lenselement of the third lens unit G3 is configured as a composite lenselement which has a resin film having an aspherical surface r₁₄ disposedon the object side surface of the lens element.

[0126] Furthermore, an aperture stop S is disposed between the firstlens unit G1 and the second lens unit G2.

[0127] The first embodiment satisfies the conditions (1), (2), (2A),(3), (3A) and (4) through (8).

[0128] The second through fifth embodiment have compositions shown inFIG. 2 through FIG. 5 respectively, each comprising a first lens unit G1having positive refractive power, a second lens unit G2 having positiverefractive power and a third lens unit G3 having negative refractivepower.

[0129] In each of zoom optical systems according to these second throughfifth embodiments, the first lens unit G1, the second lens unit G2 andthe third lens unit G3 have compositions similar to those of the first,second and third lens units in the first embodiment.

[0130] Furthermore, an aperture stop S is disposed between the firstlens unit G1 and the second lens unit G2 as in the first embodiment.

[0131] Furthermore, a most object side lens element of the third lensunit G3 is configured as an aspherical composite lens element as in thefirst embodiment.

[0132] Each of these second through fifth embodiments satisfies theconditions (1), (2), (2A), (3), (3A) and (4) through (8). In addition,each of the third, fourth and fifth embodiments also satisfies thecondition (9).

[0133] The sixth embodiment is a zoom optical system which has acomposition shown in FIG. 6 comprising, in order from the object side,first lens unit G1 having positive refractive power, a second lens unitG2 having positive refractive power and a third lens unit havingnegative refractive power.

[0134] Different from the first through fifth embodiment, the sixthembodiment uses the second lens unit G2 which consists of two cementedlens components each consisting of a negative lens element and apositive lens element, and an aperture stop S which is disposed in thesecond lens unit G2, that is, between an object side cemented lenscomponent (r₅ through r₇) and an image side cemented lens component (r₉through r₁₁).

[0135] Furthermore, the sixth embodiment satisfies the conditions (1),(2), (2A), (3), (3A) and (4) through (8).

[0136] A zoom optical system according to the seventh embodiment of thepresent invention has a composition shown in FIG. 7, comprises, in orderfrom the object side, a first lens unit G1 having positive refractivepower, a second lens unit G2 having positive refractive power and athird lens unit G3 having negative refractive power and is similar inthe composition to the sixth embodiment or uses the first, second andthird lens units G1, G2 and G3 which are similar to those in the sixthembodiment, an object side lens element of the third lens unit G3 whichis configured as an aspherical composite lens element and an aperturestop S which is disposed in the second lens unit G2.

[0137] The seventh embodiment satisfies the conditions (1), (2), (2A),(3), (3A) and (4) through (8).

[0138] The eighth embodiment of the present invention has a compositionshown in FIG. 8, and comprises a first lens unit G1 having positiverefractive power, a second lens unit G2 having positive refractive powerand a third lens unit having negative refractive power.

[0139] Though the first lens unit G1 has a composition which is the sameas that of the first lens unit in each of the first through seventhembodiments, the second lens unit G2 consists of two cemented lenscomponents (r₅ through r₇ and r₈ through r₁₀) each consisting of anegative lens element and a positive lens element and a positive lenselement (r₁₁ to r₁₂), and the third lens unit G3 consists of a positivemeniscus lens element (r₁₅ to r₁₆) having a concave surface on theobject side and a negative lens element (r₁₇ to r₁₈) which has curvatureon an object side surface higher than that on an image side surface.

[0140] Furthermore, the object side positive meniscus lens element ofthe third lens unit G3 is configured as an aspherical composite lenselement which has a resin film having an aspherical surface r₁₄ disposedon a concave surface r₁₅ of the lens element.

[0141] Furthermore, an aperture stop is disposed between the second lensunit G2 and the third lens unit G3.

[0142] The zoom optical system according to the eighth embodimentsatisfies the conditions (1), (2), (2A), (3), (3A) and (4) through (8).

[0143] The ninth embodiment comprises, in order from the object side, afirst lens unit G1 having positive refractive power, a second lens unithaving positive refractive power and a third lens unit G3 havingnegative refractive power as shown in FIG. 9.

[0144] Though the first lens unit G1 and the second lens unit G2 havecompositions similar to those of the first lens unit and the second lensunit of the eighth embodiment, the third lens unit G3 has a compositionsimilar to that of the third lens unit in the first embodiment or thelike.

[0145] In this ninth embodiment, a most object side biconcave lenselement (r₁₅ to r₁₆) of the third lens unit G3 is configured as anaspherical composite lens element which has a resin film having anaspherical surface r₁₄ disposed on an object side surface r₁₅ of thelens element, and an aperture stop S is disposed between the second lensunit G2 and the third lens unit G3.

[0146] The optical system according to this ninth embodiment satisfiesthe conditions (1), (2), (2A), (3), (3A) and (4) through (8).

[0147] The tenth embodiment has a composition shown in FIG. 10 andcomprises, in order from the object side, a first lens unit G1 havingpositive refractive power, a second lens unit G2 having positiverefractive power and a third lens unit having negative refractive power.

[0148] The first, second and third lens units G1, G2 and G3 havecompositions similar to those of the first, second and third lens unitsin the eighth embodiment, and an object side lens element (r₁₅ to r₁₆)of the third lens unit G3 is configured as an aspherical composite lenselement which has a resin film having an aspherical surface r₁₄ formedon an object side concave surface r₁₅ of this lens element.

[0149] The optical system according to this tenth embodiment satisfiesthe conditions (1), (2), (2A), (3), (3A) and (4) and (8).

[0150] An optical system according to the eleventh embodiment comprises,in order from the object side, a first lens unit G1 having positiverefractive power, a second lens unit G2 having positive refractive powerand a third lens unit G3 having negative refractive power as shown inFIG. 11.

[0151] In the eleventh embodiment, the first lens unit G1 and the thirdlens unit G3 have compositions similar to those of the first lens unitand the third lens unit of the first embodiment or the like, whereas thesecond lens unit G2 consists of two cemented lens components (r₅ throughr₇) and (r₈ through r₁₀) each consisting of a negative lens element anda positive lens element, and a positive lens element (r₁₁ to r₁₂)disposed on the image side of the cemented lens components. In theeleventh embodiment, a biconcave lens element disposed on the mostobject side in the third lens unit G3 is configured as an asphericalcomposite lens element which has a resin film having an asphericalsurface r₁₄ on an object side concave surface r₁₅ of the lens element.

[0152] Furthermore, an aperture stop S is disposed between the secondlens unit G2 and the third lens unit G3 in the eleventh embodiment.

[0153] The zoom optical system according to the eleventh embodimentsatisfies the conditions (1) through (10).

[0154] The twelfth embodiment has a composition shown in FIG. 12 andcomprises, in order from the object side, a first lens unit G1 havingpositive refractive power, a second lens unit having positive refractivepower and a third lens unit having negative refractive power.

[0155] The twelfth embodiment is similar to the ninth embodiment or thelike in compositions of the first, second and third lens units G1, G2and G3 and the like, but is different in that the twelfth embodimentuses no composite lens element.

[0156] The zoom optical system according to the twelfth embodimentsatisfies the conditions (1), (2), (2A), (3), (3A) and (4) through (7).

[0157] In the sectional views illustrating the compositions of the abovedescribed embodiments, an upper stage corresponds to the wide position,a middle stage corresponds to an intermediate focal length and a lowerstage corresponds to the tele position.

[0158] The zoom optical system according to each of the embodiments ofthe present invention can be focused from an object located at infinitedistance onto an object located as a short distance by moving only thesecond lens unit on the object side or moving only the third lens uniton the image side. Furthermore, the zoom optical system can be focusedfrom the object located at the infinite distance onto the object locatedat the short distance by moving the second lens unit on the object sideand simultaneously moving the third lens unit on the image side.

[0159] When the tenth embodiment is focused on an object distance of 80cm by moving the first lens unit and the second lens unit on the objectside and moving the third lens unit on the image side, for example, anairspace between the first lens unit and the second lens unit and anairspace between the second lens unit and the third lens unit are set aslisted below:

[0160] Wide position (f=39.2901)

[0161] Airspace between first lens unit G1 and second lens unit G2 2.94

[0162] Airspace between second lens unit G2 and third lens unit G3 16.29

[0163] Back focal length fB 6.66

[0164] Intermediate focal length (f=80.9996)

[0165] Airspace between first lens unit G1 and second lens unit G2 11.73

[0166] Airspace between second lens unit G2 and third lens unit G3 8.89

[0167] Back focal length fB 29.29

[0168] Tele position (f=164.9051)

[0169] Airspace between first lens unit G1 and second lens unit G2 15.54

[0170] Airspace between second lens unit G2 and third lens unit G3 4.94

[0171] Back focal length fB 72.62

[0172] Shapes of the aspherical surfaces used in the zoom opticalsystems according to the present invention are expressed by thefollowing formula:$x = {\frac{y^{2}/r}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( {y/r} \right)^{2}}}} + {A_{2}y^{2}} + {A_{4}y^{4}} + {A_{6}y^{6}} + \ldots}$

[0173] wherein a direction of an optical axis is taken as the x axis anda direction perpendicular to the optical axis is taken as the y axis, areference symbol r represents a radius of curvature on a referencesphere, and reference symbols A₁, A₂, A₄ and A₆, . . . designateaspherical surface coefficients.

[0174]FIGS. 13, 14 and 15 are curves illustrating aberrationcharacteristics of the first embodiment of the present invention whenthe zoom optical system is focused on an object located at infinitedistance at the wide position, intermediate focal length and teleposition respectively.

[0175] As seen from these curves, the zoom optical system according tothe present invention corrects aberrations favorably and scarcely variesthe aberrations by zooming.

[0176] Furthermore, the zoom optical system according to the secondthrough twelfth embodiments favorably correct aberrations and scarcelyvary the aberrations by zooming like the zoom optical system accordingto the first embodiment.

[0177]FIG. 16 and 17 are diagrams a zoom lens system according to thepresent invention in a condition where the zoom lens system is built ina 35 mm camera as a photographic lens system for a compact camera: FIG.16 being a perspective view and FIG. 17 being a sectional view.

[0178] In these drawings, a reference numeral 1 represents a conditionof the wide position of the first embodiment of the zoom optical systemaccording to the present invention which consists of the first lens unitG1, second lens unit G2 and third lens unit G3. A reference numeral 2designates a film, a reference numeral 3 denotes a view finder objectivelens, a reference numeral 4 represents an image erecting prism, areference numeral 5 designates an eyepiece, a reference numeral 6denotes a stop, and reference numerals 7 and 8 represent a photographingoptical path and a view finder optical path. In addition, a referencenumeral 10 designates a camera body.

[0179] This camera is configured so that the photographing optical pathand the view finder optical path are nearly in parallel with each other,and an image of an object is observed through a view finder which iscomposed of the view finder objective lens 3, the image electing prism4, the stop 6 and the eyepiece 5, and imaged photographed by a zoomoptical system 1 according to the present invention. An electronic imagepickup device such as a CCD may be used in place of the film.

[0180] The present invention makes it possible to realize a zoom opticalsystem which has a short total length at a tele position and favorableimaging performance, allows optical performance to be scarcely loweredby zooming and has a high varn-focal ratio exceeding 3.8.

1. A zoom optical system comprising, in order from an object side: afirst lens unit having positive refractive power; a second lens unithaving positive refractive power; and a third lens unit having negativerefractive power, wherein a magnification is changed from a wideposition to a tele position by moving the lens units on the object sideso as to widen an airspace between said first lens unit and said secondlens unit and narrow an airspace between said second lens unit and saidthird lens unit, and wherein said zoom optical system satisfies thefollowing conditions (1), (2), (3) and (4): (1) fT/fW>3.8 (2)0<[S(fTa)−S(fW)]/(fTa−fW)<0.2 (3) 0.8<L(fTa)/(fTa−fW)<1.05 (4)0<H(G1)/fTa<0.023 wherein reference symbols fT and fW represent focallength of the zoom optical system at the wide position and the teleposition respectively, a reference symbol fTa designates an opticalfocal length in a focal length region exceeding 3.8 times of the focallength at the wide position, a reference symbol S(fW) denotes a distanceas measured from a most object side surface to a most image side surfaceat the wide position, a reference symbol S(fTa) represents a distance asmeasured from a most object side surface to a most image side surface atthe focal length of fTa, a reference symbol L(fTa) designates a distanceas measured from the most object side surface to image at the focallength of fTa and a reference symbol H(G1) denotes a distance asmeasured from the most object side surface to a front principal point ofthe first lens unit G1.
 2. A zoom optical system comprising, in orderfrom an object side: a first lens unit having positive refractive power;a second lens unit having positive refractive power; and a third lensunit having negative refractive power, wherein a magnification ischanged from a wide position to a tele position by moving the lens unitson the object side so as to widen an airspace between said first lensunit and said second lens unit and narrow an airspace between saidsecond lens unit and said third lens unit, wherein said first lens unitconsists of two lens elements, in order from the object side, a negativemeniscus lens element which has a concave surface on the object side anda positive lens element which has an absolute value of a radius ofcurvature on an object side surface smaller than an absolute value of aradius of curvature on an image side surface, wherein said third lensunit comprises, in order from the object side, a biconcave lenscomponent, a positive lens component which has an absolute value of aradius of curvature on an object side surface smaller than an absolutevalue of a radius of curvature on an image side surface and a lenscomponent which has an absolute value of a radius of curvature on animage side surface smaller than a absolute value of a radius ofcurvature on an object side surface, and wherein said zoom opticalsystem satisfies the following conditions (2A) and (3A): (2A)0<[S(fT)−S(fW)]/(fT−fW)<0.2 (3A) 0.8<L(fT)/(fT−fW)<1.05 whereinreference symbols fW and fT represent focal lengths of the zoom opticalsystem as a whole at the wide position and the tele positionrespectively, a reference symbol S (fW) designates a distance asmeasured from a most object side surface to a most image side surface atthe wide position, a reference symbol S (fT) denotes a distance asmeasured from the most object side surface to the most image sidesurface at the tele position and a reference symbol L (fT) denotes atotal length of the optical system at the tele position.
 3. A zoomoptical system comprising, in order from an object side: a first lensunit having positive refractive power; a second lens unit havingpositive refractive power; and a third lens unit having negativerefractive power, wherein a magnification is changed from a wideposition to a tele position by moving the lens units on the object sideso as to widen an airspace between said first lens unit and said secondlens unit and narrow an airspace between said second lens unit and saidthird lens unit, wherein said third lens unit comprises, in order fromthe object side, a biconcave lens component and, a positive lenscomponent which has an absolute value of a radius of curvature on anobject side surface smaller than an absolute value of a radius ofcurvature on an image side surface and a negative lens component whichhas an absolute value of a radius of curvature on an object side surfacesmaller than an absolute value of a radius of curvature on an image sidesurface, and wherein said zoom optical system satisfies the followingcondition (10): (10) (β3T)²/[F(T)×0.03]<60 wherein a reference symbolβ3T represents a magnification of the third lens unit at the teleposition and a reference symbol F (T) designates an F number at the teleposition.
 4. A zoom optical system comprising, in order from an objectside: a first lens unit having positive refractive power; a second lensunit having positive refractive power; and a third lens unit havingnegative refractive power, wherein a magnification is changed from awide position to a tele position by moving the lens units on the objectside so as to widen an airspace between said first lens unit and saidsecond lens unit and narrow an airspace between said second lens unitand said third lens unit, and wherein said zoom optical system satisfiesthe following conditions (1), (4), (5) and (6): (1) fT/fW>3.8 (4)0<H(G1)/fTa<0.023 (5) 15<(β3T)²−(β3T)²×(β2T)²<27 (6) 0.3<f₁/fTa<0.5wherein reference symbols fW and fT represent focal lengths of theoptical system as a whole at the wide position and the tele positionrespectively, a reference symbol fTa designates an optional focal lengthin a focal length region exceeding 3.8 times of a focal length at thewide position, a reference symbol H (G1) denotes a distance as measuredfrom a first surface to a front principal point of the first lens unit,a reference symbol f1 represents a focal length of the first lens unit,and reference symbols β2T and β3T designate magnifications of the secondlens unit and the third lens unit respectively at the tele position. 5.The zoom optical system according to claim 1, 3 or 4, wherein said firstlens unit consists of two lens elements, in order from the object side,a negative meniscus lens element having a concave surface on the objectside and a positive lens element which has an absolute value of a radiusof curvature on an object side surface smaller than an absolute value ofa radius of curvature on an image side surface.
 6. The zoom opticalsystem according to claim 1 or 4, wherein said third lens unitcomprises, in order from the object side, a biconcave lens component, apositive lens compnent which has an absolute value of a radius ofcurvature on an object side surface smaller than an absolute value of aradius of curvature as on an image side surface and a negative lenscomponent which has an absolute value of a radius of curvature on anobject side surface smaller than an absolute value of a radius ofcurvature on an image side surface.
 7. The zoom optical system accordingto claim 2 or 3 satisfying the following condition (4A): (4A)0<H(G1)/fT<0.023 wherein a reference symbol fT represents a focal lengthof the optical system as a whole at the tele position, a referencesymbol H(G1) designate a distance as measured from a first surface to afront principal point of the first lens unit.
 8. The zoom optical systemaccording to claim 1, 2 or 3 satisfying the following condition (5): (5)15<(β3T)²−(β3T)²×(β2T)²<27 wherein reference symbols β2T and β3Trepresent magnifications of the second lens unit and the third lens unitrespectively at the tele position.
 9. The zoom optical system accordingto claim 1, 2 3 or 4 satisfying the following condition (6A): (6A)0.3<f₁/fT<0.5 wherein a reference symbol f1 represents a focal length ofthe first lens unit G1 and a reference symbol fT designates a focallength of the optical system and a whole at the tele position.
 10. Thezoom optical system according to claim 1, 2, 3 or 4, wherein said secondlens unit comprises at least a cemented lens component consisting of anegative lens element and a positive lens element and has negativerefractive power and a cemented lens component consisting of a negativelens element and a positive lens element and has positive refractivepower.
 11. The zoom optical system according to claim 1, 2, 3 or 4,wherein said third lens unit comprises an aspherical lens component onwhich an aspherical surface is formed by coating a concave surface of aspherical lens element with a thin resin film and wherein a shape of theaspherical surface of said aspherical lens component satisfies thefollowing condition (7) over an entire effective surface: (7)−0.2<[(1/Rb−1/Ra)/(N1−N2)]Y<0.9 wherein a reference symbol Ra representsa local radius of curvature on the aspherical surface at a height of Yas measured from an optical axis, that is, a distance of a normal to theaspherical surface at the height of Y from the optical axis as measuredfrom the aspherical surface to an intersection of the normal with theoptical axis, a reference symbol Rb designates a radius of curvature onthe optical axis of the aspherical surface, and reference symbols N1 andN2 denote refractive indices on the object side and the image siderespectively of the aspherical surface.
 12. The zoom optical systemaccording to claim 11, wherein the shape of the aspherical surface ofsaid aspherical lens component satisfies, in place of the condition (7),the following condition (7-1) over the entire effective surface: (7-1)−0.1<[1/Rb−1/Ra]/(N1−N2)Y<0.4 wherein a reference symbol Ra represents alocal radius of curvature on the aspherical surface at a height of Y asmeasured from an optical axis, that is, a distance of a normal to theaspherical surface at the height of Y from the optical axis as measuredfrom the aspherical surface to an intersection of the normal with theoptical axis, a reference symbol Rb designates a radius of curvature onthe optical axis of the aspherical surface, and reference symbols N1 andN2 denote refractive indices on the object side and the image siderespectively of the aspherical surface.
 13. The zoom optical systemaccording to claim 2, wherein an Abbe's number υ_(d)(1R) of a positivelens element disposed on the most image side in said first lens unitsatisfies the following condition (8): (8) υ_(d)(1R)>81
 14. The zoomoptical system according to claim 1, 3 or 4 wherein said first lens unitcomprises a positive lens element on a most image side and an Abbe'snumber υ_(d)(1R) of said positive lens element satisfies the followingcondition (8): (8) υ_(d)(1R)>81
 15. The zoom optical system according toclaim 1, 2, 3 or 4, wherein said third lens unit comprises a lenselement which has an aspherical surface and a resin film having anaspherical surface is disposed on said lens component having theaspherical surface.
 16. The zoom optical system according to claim 15,wherein said resin film satisfies the following condition (9): (9)K<0.01 wherein a reference symbol K represents a water absorption ratioof the resin film.
 17. The zoom optical system according to claim 1, 2,3 or 4, wherein an aperture stop is disposed between said first lensunit and said second lens unit.
 18. The zoom optical system according toclaim 1, 2, 3 or 4, wherein an aperture stop is disposed in said secondlens unit.
 19. The zoom optical system according to claim 1, 2, 3 or 4,wherein an aperture stop is disposed between said second lens unit andsaid third lens unit.
 20. A camera comprising: a photographic opticalsystem; and a view finder optical system arranged nearly in parallelwith an optical path of said photographic optical system, wherein thezoom optical system according to claim 1, 2, 3 or 4 is used as saidphotographic optical system.